A weakness of the Qt DRT setup is that things like JSContextRef are abstracted
away from the QtWebKit API so we need DumpRenderTreeSupportQt to access WebCore internals.
Since the window.internals object requires JSContextRef we need to implement it in DumpRenderTreeSupportQt
where we can access it. DumpRenderTreeSupportQt cannot be compiled outside Qt's WebCore and as it
is our only possible route into the WebCoreTestSupport class neither can the new window.internals plumbing.
Likewise we can't put the accessor in WebCoreTestSupport because it would then need to know about QWebFrame
and others. The only alternative seems like a compile time guard which we would have to teach the bots about.